diff mbox

[net] dccp: fix out of bound access in dccp_v4_err()

Message ID 1478138440.7065.419.camel@edumazet-glaptop3.roam.corp.google.com
State Accepted, archived
Delegated to: David Miller
Headers show

Commit Message

Eric Dumazet Nov. 3, 2016, 2 a.m. UTC 
From: Eric Dumazet <edumazet@google.com>

dccp_v4_err() does not use pskb_may_pull() and might access garbage.

We only need 4 bytes at the beginning of the DCCP header, like TCP,
so the 8 bytes pulled in icmp_socket_deliver() are more than enough.

This patch might allow to process more ICMP messages, as some routers
are still limiting the size of reflected bytes to 28 (RFC 792), instead
of extended lengths (RFC 1812 4.3.2.3)

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/dccp/ipv4.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

Comments

David Miller Nov. 3, 2016, 8:20 p.m. UTC | #1 
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Wed, 02 Nov 2016 19:00:40 -0700

> From: Eric Dumazet <edumazet@google.com>
> 
> dccp_v4_err() does not use pskb_may_pull() and might access garbage.
> 
> We only need 4 bytes at the beginning of the DCCP header, like TCP,
> so the 8 bytes pulled in icmp_socket_deliver() are more than enough.
> 
> This patch might allow to process more ICMP messages, as some routers
> are still limiting the size of reflected bytes to 28 (RFC 792), instead
> of extended lengths (RFC 1812 4.3.2.3)
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied and queued up for -stable.
diff mbox

Patch

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 345a3aeb8c7e..32f00ffdbf42 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -235,7 +235,7 @@  static void dccp_v4_err(struct sk_buff *skb, u32 info)
 {
 	const struct iphdr *iph = (struct iphdr *)skb->data;
 	const u8 offset = iph->ihl << 2;
-	const struct dccp_hdr *dh = (struct dccp_hdr *)(skb->data + offset);
+	const struct dccp_hdr *dh;
 	struct dccp_sock *dp;
 	struct inet_sock *inet;
 	const int type = icmp_hdr(skb)->type;
@@ -245,11 +245,13 @@  static void dccp_v4_err(struct sk_buff *skb, u32 info)
 	int err;
 	struct net *net = dev_net(skb->dev);
 
-	if (skb->len < offset + sizeof(*dh) ||
-	    skb->len < offset + __dccp_basic_hdr_len(dh)) {
-		__ICMP_INC_STATS(net, ICMP_MIB_INERRORS);
-		return;
-	}
+	/* Only need dccph_dport & dccph_sport which are the first
+	 * 4 bytes in dccp header.
+	 * Our caller (icmp_socket_deliver()) already pulled 8 bytes for us.
+	 */
+	BUILD_BUG_ON(offsetofend(struct dccp_hdr, dccph_sport) > 8);
+	BUILD_BUG_ON(offsetofend(struct dccp_hdr, dccph_dport) > 8);
+	dh = (struct dccp_hdr *)(skb->data + offset);
 
 	sk = __inet_lookup_established(net, &dccp_hashinfo,
 				       iph->daddr, dh->dccph_dport,